Repeat sequence proteins as matrices for nanocomposites

Recombinant protein–inorganic nanocomposites comprised of exfoliated Na⁺ montmorillonite (MMT) in a recombinant protein matrix based on silk-like and elastin-like amino acid motifs (silk elastin-like protein (SELP)) were formed via a solution blending process. Charged residues along the protein backbone are shown to dominate long-range interactions, whereas the SELP repeat sequence leads to local protein/MMT compatibility. Up to a 50% increase in room temperature modulus and a comparable decrease in high temperature coefficient of thermal expansion occur for cast films containing 2–10 wt.% MMT.     

Best of Both Worlds: Synergistically Derived Material Properties via Additive Manufacturing of Nanocomposites

With an exponential rise in the popularity and availability of additive manufacturing (AM), a large focus has been directed toward research in this topic's movement, while trying to distinguish themselves from similar works by simply adding nanomaterials to their process. Though nanomaterials can add impressive properties to nanocomposites (NCs), there are expansive amounts of opportunities that are left unexplored by simply combining AM with NCs without discovering synergistic effects and novel emerging material properties that are not possible by each of these alone. Cooperative, evolving properties of NCs in AM can be investigated at the processing, morphological, and architectural levels. Each of these categories are studied as a function of the amplifying relationship between nanomaterials and AM, with each showing the systematically selected material and method to advance the material performance, explore emergent properties, as well as improve the AM process itself. Innovative, advanced materials are key to faster development cycles in disruptive technologies for bioengineering, defense, and transportation sectors. This is only possible by focusing on synergism and amplification within additive manufacturing of nanocomposites.     

Sorption of phenols onto sandy aquifer material: the effect of dissolved organic matter (DOM)

The influence of dissolved organic matter (DOM) on the sorption of four phenols, 2,4,6-trichlorophenol (2,4,6-TCP), pentachlorophenol (PCP), 2,4-dinitrophenol (2,4-DNP) and 2-methyl-4,6-dinitrophenol (2-M-4,6-DNP), onto sandy aquifer material at different pH values was investigated using flow through column experiments. The pH-dependent sorption of the chlorinated phenols 2,4,6-TCP and PCP was not significantly affected by DOM (measured as dissolved organic carbon, DOC), whereas in the case of nitrophenols a significant lower retardation was found, depending on the DOC concentration and pH value of the aqueous solution. Sorption decreases with increasing DOC concentration, which indicates a binding of these compounds by DOM. The degree of sorption reduction depends on the pH value and increases with increasing fraction of neutral species. The different behaviour of nitrophenols in comparison to the chlorophenols is assumed to be a result of specific charge-transfer interactions. A combined sorption and complex formation model was used to describe the effect of pH and DOC concentration on the sorption of nitrophenols onto aquifer material and to estimate binding coefficients of neutral nitrophenols on DOM.     

Glycerol monocaprate (monocaprin) reduces contamination by Escherichia coli and Salmonella enteritidis on hard surfaces

Emulsions of glycerol monocaprate (monocaprin) kill a variety of pathogenic bacteria and viruses in suspension. In this study the microbicidal activity of monocaprin against enterobacteria was tested on contaminated hard surfaces. Surfaces were contaminated with nutrient broth or meat juice containing large numbers of Escherichia coli or Salmonella enteritidis. They were then treated with acidified monocaprin emulsions and the surviving bacteria counted. Monocaprin killed S. enteritidis in chicken meat juice on plastic cutting boards and reduced the number of viable E. coli and S. enteritidis by more than 5 log₁₀ in 2 min on a laminated plastic kitchen counter contaminated with nutrient broth. Monocaprin rapidly killed E. coli on glass, stainless steel, laminated plastic, glazed ceramic tiles and polypropylene boards. It was most effective on glass and stainless steel and more effective on dry than on wet surfaces. It was concluded that acidified monocaprin emulsions reduce contamination by pathogenic enterobacteria on hard surfaces. They may be useful as sanitizers in the home, and possibly in public places, where contaminated surfaces are a potential source of transmission of pathogens to humans. Cleaning with monocaprin emulsions may therefore be a means to improve hygiene and infection control.     

Polymer design for high temperature shape memory: Low crosslink density polyimides

Shape memory in polymers is a process whereby mechanical energy is microscopically stored, and reversibly recovered within the polymer. Consideration of the viscoelastic and glassy dynamics necessary for each step of the process reveals key molecular characteristics that may improve performance, including a rigid polymer backbone with narrow molecular weight distribution between a low fraction of crosslinks. With this insight to guide high temperature polymer design, aromatic CP2 polyimide and associated single wall carbon nanotube (SWNTs) nanocomposites are shown to have excellent shape memory performance at 220 °C with rapid recovery (<10 s), excellent fixity (>98%), good cyclability and outstanding creep resistance. A narrow glass transition temperature regime (<10 °C) and high fragility (m ～ 117) affords a narrow triggering window and the ability to spatially localize recovery with a temperature gradient. The addition of up to 3 vol% of dispersed SWNTs improves the rubbery modulus and blocking force without substantially impacting these crucial characteristics. The structure-performance relationships in this material system reinforce the key molecular characteristics for the design of polymers for shape memory.     

Racemization‐Free Chemoenzymatic Peptide Synthesis Enabled by the Ruthenium‐Catalyzed Synthesis of Peptide Enol Esters via Alkyne‐Addition and Subsequent Conversion Using Alcalase‐Cross‐Linked Enzyme Aggregates

The C‐terminal activation of peptides as prerequisite for the formation or ligation of peptide fragments is often associated with the problem of epimerization. We report that ruthenium‐catalyzed alkyne addition with (+)‐2,3‐O‐isopropylidene‐2,3‐dihydroxy‐1,4‐bis(diphenylphosphino)butane as ligand allows the racemization‐free synthesis of peptide enol esters tolerating a wide range of functional groups. The transformation can be performed in a variety of different solvents addressing the solubility issues imposed by peptides with varying amino acid side chain patterns. We show that peptide enol esters with an amide motif in the enol moiety are excellent acyl donors for the peptide condensation with other peptide fragments in organic solvents using serine endopeptidase subtilisin A as catalyst. The reported combination of transition metal catalysis with enzymatic peptide ligations adds an important tool for the racemization‐free synthesis and ligation of peptides which is compatible even with unprotected amino acid side chains.     

Kinetics of Z-Phase Precipitation in 9 to 12 pct Cr Steels

The Z-phase nitride is seen as a detrimental phase in 9 to 12 pct Cr steels as it is in competition with the beneficial MX particles. Two model steels, with 9 pct Cr and 12 pct Cr content, respectively, were designed to study the effect of Cr on Z-phase precipitation kinetics. The steels were isothermally aged at 873 K, 923 K, and 973 K (600 °C, 650 °C, and 700 °C) for up to 30,000 hours in order for Z-phase to replace MX. X-ray diffraction (XRD) analysis of extracted precipitates was used to quantitatively follow the evolution of the nitrides population. It was found that the 12 pct Cr steel precipitated Z-phase 20 to 50 times faster than the 9 pct Cr steel. Transmission electron microscopy (TEM) was applied to follow the Z-phase precipitation, using energy-dispersive X-ray spectroscopy (EDS) line scans and atomic resolution imaging.     

Conversion of MX nitrides to Z-phase in a martensitic 12% Cr steel

A 12% Cr model steel was designed with the purpose of studying the nucleation and growth of modified Z-phase, Cr(V,Nb)N. The model alloy develops Z-phase after relatively short ageing times and contains only nitrides of Cr, V and Nb. Interferences from the presence of carbides and the development of Laves phase were avoided by keeping the C, W and Mo contents as low as possible. Transmission electron microscopy and X-ray diffraction analysis of extracted particles were used to follow the evolutions of phase composition, phase morphology and phase fraction, particularly of the precipitation of Z-phase, during ageing at 600, 650 and 700 °C for up to 10³ h. The development of Z-phase appears to be accomplished by the diffusion of Cr atoms into (V,Nb)N particles and their subsequent conversion into cubic or tetragonal Z-phase. Studies at various temperatures indicate that Z-phase development proceeds fastest at 650 °C and that Z-phase forms faster at prior austenite grain boundaries.